1. Object of the Invention
This invention relates to an emergency cable gripper suitable for preventing the loss of guys or cables on a guyed offshore petroleum drilling or production structure. More particularly, the invention relates to a novel apparatus employing wedges to grip the cable and hold it stopped in its protective tube. A cable clamp and stopping ram are used to automatically actuate the gripping wedges in case of an accident. The apparatus is operable under water.
2. Field of the Invention
The ever more difficult search for petroleum has led to exploration in areas previously thought by many to be incapable of producing oil at economically feasible prices. The rising price of petroleum has made acceptable the costs associated with production in Alaska and the North Sea, as well as in the near-offshore areas of North America. Petroleum exploration and production in each of these areas has created problems, both esoteric and mundane, which must be solved. This invention is concerned with the solution of a potential safety problem on an offshore structure.
One of the many structures used in offshore drilling and production is one known as the "guyed tower". Simply stated, it is a space frame construction which may stand in 1500 feet or more of water, is footed in the seabed, and has a deck above the water level. Drilling and production equipment, sleeping quarters, helicopter landing pads, etc. are positioned on the deck. It is denominated a "guyed" tower because of the guylines which hold it upright and relatively immobile. A generalized discussion of guyed towers is found in U.S. Pat. No. 3,903,705, to Beck et al. Guylines on guyed towers are often "held off" at or near the deck by clamps. A guyline, as it passes down from the deck, ideally is channelled through either a leg of the structure or a guyline protection tube (which may be oil-filled) and in either event exits the structure below the water surface through an apparatus known as a "fairlead". Fairleads have the function of directing the guyline in the direction of the anchoring means. The anchoring means exemplarily comprise a clump weight of up to 100 tons or more and is in turn connected to two anchors in series. An anchor pendant and anchor buoy often are used to indicate the position of the anchors.
The instant invention relates specifically to the solution of a safety problem on a guyed tower although the invention apparatus has a broader application to any apparatus having guy wires.
It is not difficult to appreciate the desirability of protecting the guylines from accidental loss. If the guylines are dropped from the deck's surface as the result of a fire or mishandling of the clamps, the structure could shift, bringing drilling and production operations into jeopardy, or, in a natural catastrophe such as a hurricane, topple the structure.
Several methods of gripping wire cable or rope are shown. A number of those methods are said to be suitable for emergency gripping service.
A cable locking device to be used in a passenger safety belt apparatus is disclosed in U.S. Pat. No. 3,147,527, to Gilmore. The locking device utilizes a deformable conical ferrule crimped to the cable at some desired point along the cable length. A quick but powerful jerk on the cable is needed to move the crimped ferrule and the cable into the larger end of a tapered serrated sleeve mounted, in turn, inside the mouth of a larger housing. The ferrule deforms and is squeezed in a permanent grip between the serrated sleeve and the cable. The cable gripping wedges of the instant invention are not substantially deformable, are designed to be reusable, and easily disengaged from the cable.
The invention described in U.S. Pat. No. 3,467,224, to Curtis et al, is a hydraulically operated device used for gripping an oil derrick "cat line" in an emergency. The apparatus uses two approximately wedge-shaped members which are activated either manually by a human operator on the drilling deck or automatically by a mechanism which detects a broken cable whipping to-and-fro. This apparatus does not utilize the weight of the cable to self-activate as does the device of the present invention.
Another device suitable for catching a broken wire cable is shown in U.S. Pat. No. 3,779,347, to Chevalier. The cable catcher uses a pair of wedges placed in series to squeeze the cable against a stationary braking shoe. The device allows the cable to move freely in one direction and relies on friction with the cable to prevent any movement in the other direction. In contrast, the device disclosed herein does not rely on constant contact with the cables, with the attendant probability of wear, to actuate the gripping mechanism.
A cable-anchoring mechanism described in U.S. Pat. No. 3,952,377, to Morell, utilizes a conical wedge permanently attached to a wire cable. The wedge, in turn, fits inside a fixed sleeve. The device is said to be useful as an anchor for concrete-reinforcing tendons. The wire cable must always carry the fixed conical wedge thereby limiting the motility of the wedge and causing additional stress on the wire cable.
Another cable gripping device using conical wedges is shown in U.S. Pat. No. 4,078,277. The conical wedges are split down the middle and have grooves suitable for engaging the twist of the wire cable. The two wedges contiguously fit within a cone-shaped sleeve. The wedge-sleeve assembly is inserted in a suitably sized orifice and maintained under tension. Slackening of the wire cable will cause disassembly of the clamp.